1. Technical Field
The present disclosure relates to orthopedic screw systems for bone fixation, and more particularly, to providing facet joint fixation screw systems with anti-backout features which prevent unintentional withdrawal of the screw and instrument systems to facilitate minimally invasive screw placement.
2. The Relevant Technology
Loosening is a commonly encountered problem with screw fixation. A screw may work its way loose over time, such that fixation is compromised or the screw head protrudes to an undesirable extent from the surrounding material. Loosening is seen in orthopedic applications, such as facet joint fixation or facet joint fusion, at least partially because normal physiologic movement tends to encourage screw migration, and the bone into which the screw is driven tends to remodel over time. The three-dimensional topography of the bone surface presents an additional challenge in achieving secure fixation. The present disclosure provides a low-profile, self-contained, polyaxial, one-way screw and washer system that automatically and continuously resists any tendency of the screw to unthread from the surrounding material.
Bone screws may be inserted with a minimally invasive surgical technique. An example of a minimally invasive surgical technique is one in which the surgical exposure is minimized. Bone screws may be inserted through a surgical exposure which forms a passageway between the skin incision and a target location on a bone. The passageway may be oriented along a final implantation trajectory of the screw, i.e., along a center longitudinal axis of the screw. The width of the passageway may be only slightly greater than the outer dimension of the screw, a corresponding screwdriver, or other system component. The passageway may be held open by a tube or cannula. The cannula may also protect surrounding tissues from collateral damage during the surgical procedure of inserting the screw. The present disclosure provides a cannula insertion system for forming a passageway and holding the passageway open during the surgical procedure.